Physical Plasma Elicits Immunogenic Cancer Cell Death and Mitochondrial Singlet Oxygen

Plasma oncotherapy receives increasing attention due to considerable success in preclinical research. Different plasma sources were shown to induce cancer cell death in vitro and in vivo. Plasmas for medicine expel reactive species of many kinds. These have been implicated in the induction of immunogenic cancer cell death that increases the visibility of killed cells to the immune system. Cell membrane-bound calreticulin (CRT) serves as key damage-associated molecular pattern molecule to elicit antitumor immune responses. To investigate CRT translocation upon challenge with medical plasma, CT26 colon cancer cells were treated in vitro using the atmospheric pressure argon plasma jet kINPen. Cells underwent apoptosis, which was accompanied by exposure of CRT. Interestingly, CRT was upregulated on viable as well as dead cells, and remained upregulated up to 72 h post-treatment. Cell death was preceded by loss of membrane potential in mitochondria. These endosymbionts are capable of generating singlet oxygen, a molecule that has been suggested to drive radical chains in plasma cancer cell death. Using fluorescent probes, we identified a role of endogenous (mitochondrial-derived) over exogenous (plasma-derived) singlet oxygen in plasma-treated cancer cells.